The present invention relates to lubrication of bearing assemblies, and in particular, to lubrication of an inner ring of angular contact ball bearings assemblies, such as those used in gas turbine engines.
Bearing assemblies are integral to the performance and speed of gas turbine engines. To keep bearing assemblies lubricated and cool, it is essential that lubricating fluid, such as oil, be delivered to the bearing assemblies. Ball bearing assemblies comprise an array of spherical ball bearing elements that roll between inner and outer rings. In gas turbine engines, an engine shaft is typically inserted into the inner ring, while the outer ring is secured to a stationary strut. Thus, the inner ring rotates with the shaft as the ball bearing elements roll along the inner and outer rings.
Conventional under-race oil delivery systems provide oil to the bearings by delivering the oil to the inner diameter surface of the inner raceway from under the inner ring. Typically, a hole connects the inner diameter surface of the inner ring the outer diameter surface of said ring, allowing lubricating oil to pass through the ring. In this manner, lubricating oil can be passed to either the raceway of the inner ring or to the shoulder of the inner ring where the bearing cage contacts the inner ring. In some cases a spacer having axial slots is used to allow the oil to flow between the shaft and the inner diameter of the inner ring. Inclusion of this spacer, however, can have a negative impact on the performance of the bearing or its ability to fit into a limited space. Inclusion of the spacer requires that the bearing assembly be at a larger diameter than it would be without the spacer. As a consequence, the ball bearing elements are rotating at a larger pitch diameter. Larger pitch diameters lead to larger stresses from centrifugal forces and reduced thrust capacity in the bearing assembly, particularly for high speed applications. Inclusion of the spacer also requires that the outer diameter of the bearing be increased. In applications with limited radial space, removal of the spacer under the bearing might be beneficial. Thus, it is desirable to reduce the pitch diameters in bearing assemblies.